1. Field of the Invention
The present invention relates to a projection lens assembly, for example, for enlarging a projection, which has an F No (f-number) of approximately 1:4-1:4.8, and a half field angle of around 40.degree., and in which a good performance can be obtained in a wide variable power range. The present invention also relates to a projector using such a projection lens.
2. Description of Related Art
To project a picture of a large size, it is known that one must project a small image of modulating elements on to a screen in an enlarged scale. In this projection system, separate B (blue), G (green) and R (red) images are combined by a color combining prism or the like, as disclosed, for example, in the Japanese Unexamined Patent Publication (Kokai) No. 2-40607.
However, the recent developments in the field of machining technology, regarding liquid crystal (of which an image modulating element is made), has enabled the provision of a color image, of high resolution, using just one liquid crystal modulating element. Consequently, no space is required for accommodating the color combining prism, as disclosed in JPP '067 mentioned above. Nevertheless, there is still a need for an increase in the angle of view, a decrease in the size, and a reduction in the manufacturing cost, for a projector.
Moreover, it is preferable that illuminating light is collimated light, in view of the dependency of a liquid crystal upon angle. However, it is necessary to use a large diameter lens in order to receive the collimated light, which is transmitted through the liquid crystal. To this end, it is widely known, to use a condenser lens to thereby realize a small image forming lens system. A condenser lens for a super wide angle lens has a strong power, and accordingly must be made of a Fresnel lens, from the viewpoint of space and optical performance.